1. Field of the Invention
This application relates to the drilling of wells in the production of oil, gas, and other fluids from underground formations, and particularly to the stabilization of boreholes drilled for the production of hydrocarbons. It includes the treatment of shale and clay in situ to prevent swelling caused by the absorption of water from drilling fluids.
2. Description of the Related Art
A good description of the problem which this invention addresses in the context of formation drilling may be found in an article by Thomas W. Beihoffer, et al. in the May 16, 1992 Oil & Gas Journal, page 47 et seq., entitled “Cationic Polymer Drilling Fluid Can Sometimes Replace Oil-based Mud.” As stated therein, “(S)hales can become unstable when they react with water in the drilling fluid. These reactive shales contain clays that have been dehydrated over geologic time by overburden pressure. When the formation is exposed, the clays osmotically imbibe water from the drilling fluid. This leads to swelling of the shale, induced stresses, loss of mechanical strength, and shale failure.” Shale crumbling into the borehole (“sloughing”) can ultimately place a burden on the drill bit which makes it impossible to retrieve.
Salts such as potassium chloride have been widely used in drilling treatments to convert the formation material from the sodium form by ion exchange to, for example, the potassium form which is less vulnerable to swelling. Also, the use of high concentrations of potassium salts affects the osmotic balance and tends to inhibit the flow of water away from the high potassium salt concentrations into the shale. However, it is difficult to maintain the required high concentrations of potassium salts in the drilling fluids. In addition, the physical introduction of such salts causes difficulties with the preparation of the viscosifying materials typically used for drilling. Inorganic salts can also have a harmful effect on the environment if released.
As background for the present disclosure, I have assembled prior art references representative of three general types of amine and quaternary ammonium cation sources which have been suggested for clay treatment in hydrocarbon recovery. These are (a) single-site quaternaries and amines, (b) compounds having a few (two to about six) amine or quaternary ammonium cation sites, which I have called “oligocationic”, and (c) quaternary ammonium or amine polymers, which may have from about six to thousands of cationic sites. The entire specifications of all of the patents set forth below are incorporated by reference, as the cationic materials described therein are useful in my invention.
A. Single-Site Quaternaries and Amines: Brown, U.S. Pat. No. 2,761,835; Brown, U.S. Pat. No. 2,761,840; Brown, U.S. Pat. No. 2,761,836; Himes, et al., U.S. Pat. No. 4,842,073; Thomas and Smith, U.S. Pat. No. 5,211,239.
B. Oligocationics: Brown, U.S. Pat. No. 2,761,843; Krieg, U.S. Pat. No. 3,349,032.
C. Polycationics: Borchardt, et al., U.S. Pat. No. 4,447,342; McLaughlin, et al., U.S. Pat. No. 4,374,739; McLaughlin, et al., U.S. Pat. No. 4,366,071.